In December, to the delight of many cardiologists and the dismay of many doughnut lovers, the New York City Board of Health voted to ban artificial trans fats from restaurants, school cafeterias, pushcarts, and almost every other food-service establishment it oversees, which includes most everything except hospitals. Trans fats don’t occur naturally in the things people like but feel guilty eating, or at least not at high levels (there are small proportions in the fat in meat and dairy products). But artificial ones are plentiful in commercial foods, because they are easy to use, cheaper than natural fats, and keep practically forever. Trans fats are made by pumping hydrogen gas into liquid fats usually in the presence of nickel so that they will remain solid at room temperature, like butter and lard; and they have the same wonderful properties in pie crusts, cookies, and cakes. Crisco, still generic for solid shortening made by partial hydrogenation (of cottonseed oil), soon became the “sanitary” choice for pie crust and fried chicken, making pastry almost as flaky and skin almost as crisp as lard does.

But starting in the 1970s, a time of general fat panic related to heart disease, trans fats began to look as bad for cholesterol levels as the dreaded saturated fats, and in the 1990s the picture got worse. Trans fats, long-term studies reported, not only raise “bad” cholesterol (LDL); they also lower “good” cholesterol (HDL)—which not even saturated fats do. They look about as bad for the arteries as a fat can be. A 2002 consensus report from the National Academies of Sciences’ Institute of Medicine called the relationship between trans-fat consumption and coronary heart disease “linear” and stated that the only acceptable level of trans fats in the diet was zero. The next year the Food and Drug Administration required food processors to list trans-fat levels on nutrition labels along with saturated fat. When the rule went into effect, in January 2006, public awareness of trans fats went up, and the stage was set for the New York City ban.

Thomas Frieden, New York’s health commissioner, was already unpopular among libertarians. An epidemiologist and doctor whose speciality is infectious disease, he advocates the blunt instrument of regulation, often over the current public-health approach to most problems, which emphasizes education programs that encourage people to make healthy choices. Frieden made international news by leading the charge to pass the city’s comprehensive smoking ban, which has been duplicated across the country and the world. He believes that government should make the healthful choice the default, and that eliminating trans fats will do that, just as fluoridating water and getting the lead out of paint did.

Why an outright ban? Asking nicely didn’t work. Starting in June of 2005, the city sent information on why and how to avoid trans fats to 30,000 restaurants and food-service establishments and to 200,000 clinics and community centers; it also provided training to 7,800 restaurant operators. A year later, the share of food-service establishments using trans fats—half—hadn’t budged. With the support of Michael Bloomberg, Frieden’s health-conscious boss, the city’s board of health passed the proposed ban.

Libertarians were newly displeased, as legislators in California and Massachusetts began calling for similar bans. Chicago, which last summer enacted a widely ridiculed (and flouted) ban on foie gras, was also said to have trans fats in its sights. Columnists began asking exasperated what-next questions: Salt, a perennial runner-up to fat in the sin sweepstakes? Sugar? Whole milk? Alcohol, again?

Boston, with a similarly activist commissioner and a bold, public-health-minded mayor, Thomas M. Menino, was reported to be the next large city considering a ban. That commissioner, John Auerbach, is my spouse, so I followed the debate closely. I attended a meeting of the Boston Public Health Commission board (a meeting open to the public and press) and listened to the drafters of the New York ban narrate a PowerPoint presentation by conference call. The board was interested in the practicalities of enforcing the ban. I was interested in the practicalities of how small-business owners could follow the new rules—and how cooks could give customers the flavors and textures they were used to.

The New York presenters were reassuring, if short on details. Restaurant inspectors would simply add questions about trans fats to their normal checklist, scanning menus for items likely to contain them—say, cake mixes and frozen french fries—and asking to see labels for all cooking fats. It would add just a few minutes to the usual hour-long inspection. As for telling restaurants how to substitute other fats and where to buy them, the health department planned to contract with culinary educators to teach at workshops and to staff technical-assistance help lines.

It seemed clear that restaurants would be left with plenty of questions, and I had a few of my own. I made an appointment to talk to Frieden, and to see several cooks whose businesses would be significantly affected by the ban. I also learned a lot about doughnuts— including that I like them more than can be good for me, whatever the fat.

A youthful forty-six, and thin, as you would expect, Frieden is both plainspoken and sure he is right. The morning I visited him, in the health department’s WPA-era headquarters in Lower Manhattan, he told me that he and his communications director, Geoffrey Cowley, had just been wondering why his initiatives were so frequently “mis-spun” as the work of the “nanny state.” He pre-sents himself more as an emergency repairman. Little of what he does, he said, “would be necessary if our health-care system worked—if every person had a doctor, continuity of care, and that doctor had access to their records.” Better labels are all well and good, but “we don’t want to exhort people to look at labels for trans fat,” he said. “We want people to walk into a restaurant and not worry there’s an artificial chemical in their food” that is killing them. A city trans-fat ban, he says, could prevent 500 premature deaths a year from heart disease.

I asked Frieden if he was trying to do what the federal government would not: force fast-food chains to remove trans fats. Kentucky Fried Chicken has already replaced its trans fats, as has Wendy’s; Disney, Starbucks, and other companies have also gotten on the bandwagon. But McDonald’s has been dragging its heels. It loudly announced, in 2002, that it would remove trans fats from all its food, but never got around to taking them out of its french fries—by far the biggest source, and the greatest challenge for texture (the original fat in McDonald’s french fries was the lard-like beef tallow). Now it and every other chain unwilling to abandon the New York City market will have to reformulate their menus, and given research costs and economies of scale, the changes are likely to be national, not just regional. “Nothing like a deadline to focus the mind,” Frieden said.

Wasn’t New York’s ban a case of governing the country from one city—and wasn’t it really aimed at obesity? Frieden emphatically rejected the idea, saying that his fiduciary responsibility was solely to the citizens of New York City. The ban was meant to reduce premature deaths from heart disease, no more and no less. And he wasn’t depriving people of pleasure. “We’re not going to desalinate New York,” he said, although he sounded as if he’d like to. “We’re not going to ban eggs and ham.” The science on trans fats, he said, had come clear slowly, as had the science on the effects of secondhand smoke. But once it did, it did decisively, and he had to act.

So far, the chains that have initiated trans-fat removal have been the ones whose image depends on health or whose owners are concerned with health: the Tennessee-based Ruby Tuesday; the Boston-based Legal Sea Foods (whose owner, Roger Berko­witz, has long been ahead of every health curve); and Au Bon Pain, another Boston-based chain.

When I visited Au Bon Pain’s headquarters and test kitchen, the head baker, Harold Midttun, told me that he had sold his family bakery after a heart attack at age thirty-nine. Once he got to Au Bon Pain, he took immediate interest in its mission to find substitutes for trans fats in cookies, muffins, and bagels; with Thomas John, the executive chef, and John Billingsley, the chief operating officer, he organized many tastings to sample new formulations alongside the originals. What were the tastings like? I asked the three men. Fattening, Billingsley replied.

Breads and even muffins were relatively simple; cookies were not. Chocolate-chip cookies, for instance, need the snap and solid texture that butter—or shortening, its much less expensive substitute—gives them when they cool. The company intended to “be zero trans fat” by April of this year, but not all the strudel problems (or the cream-soup ones, for that matter) had been solved.

I realized that saying trans fats are “totally replaceable,” as Frieden repeatedly does—asserting that they are merely used for texture, not taste—is easier for a health official than for a product developer. It should be simple, yes, to get rid of an entirely artificial ingredient that is used mostly for the convenience of industry. Researchers have been working for decades on substitutes, which should by now be as plentiful and as cheap as trans fats.

But they’re not. Midttun and John gave the example of their blueberry muffins, which used to be the highest in trans fats, as a challenge they had finally met. They did it by using a new fat and adding several other ingredients to mask its taste and still get the same mouthfeel. The ingredients, they told me, included oat bran, ground golden flaxseed, soy protein, and emulsifiers. Individual bakers, I thought, were sunk: They’d never be able to figure all that out, even with frequent calls to a city help line.

And the substitute fats have problems of their own. Earth Balance, a blend that Au Bon Pain uses, includes some palm-fruit oil, which is 50 percent saturated. Very highly saturated tropical oils, like coconut, were the target of a widely publicized 1994 exposé of movie popcorn by the Center for Science in the Public Interest. Now, the current thinking runs, saturated fats are not quite as bad for you as trans fats—but they’re still bad, and the American Heart Association has expressed concern about using them as a substitute for trans fats.

Dunkin’ Donuts, another national chain based in the Boston area, says that it has tried twenty-two different fats in sixty-seven tests, hoping to get the same texture its doughnuts now have. Recognizing the difficulty posed by doughnuts and other fried doughs, New York modified its regulation to give doughnut makers eighteen months to come up with suitable alternatives. If Dunkin’ has found a good substitute, it isn’t saying.

Doughnut Plant, a cult fry shop on Manhattan’s Lower East Side, is a poster child for the ban: It proudly announces that it fries only in corn oil (see “Doughnut Heaven,” page 122). Mark Isreal, the eccentric, garrulous owner, certainly doesn’t compromise on quality or expertise with his doughnuts. When I went to see him, I found myself following Frieden’s example: He told me that at a health-department staff gathering after the ban was passed, he “couldn’t stop eating” Isreal’s doughnuts.

But when I tried similar flavors at Dunkin’ Donuts, I saw why lard and solid shortening have always been best for deep frying (Dunkin’ has never used lard): The resolidified fat gives the interior a texture that oil simply cannot. Yeast-raised doughnuts are less problematic, because they should remain airy. But in a cake doughnut, the right texture is as unmistakable as the firm crumble of a butter cake—which, of course, requires a fat that solidifies at room temperature. A good cake doughnut has the substance of pound cake. It won’t get that from corn or canola oil.

It’s a confusing picture. Looking into trans fats got me hooked on an extremely fatty food I hadn’t eaten since childhood (positively unpatriotic, as John T. Edge’s monograph Donuts: An American Passion engagingly makes clear). Frieden readily admits that banning trans fats won’t help reduce obesity. Posting calorie counts where you pay for your food—a less-noticed regulation he got passed at the same time as the trans-fat ban—might help. Or it might just make people eat more doughnuts: A Dunkin’ Donuts glazed yeast doughnut has 180 calories, a glazed cake doughnut has 350, a reduced-fat blueberry muffin has 400, and a corn muffin has 510. Getting people to eat less fat and more fresh and unprocessed food—the real path to health—can’t be done by any regulation yet proposed by the “food police.”

Still, it does seem like a good idea to remove artificial substances from the food supply, especially if trans fats result in thousands of needless deaths a year. And the international headlines the initiative produced will most likely make people think more about the healthfulness of the food they eat, and restaurateurs about what they put into their food, all for a relatively modest expenditure on the city’s part. As my spouse points out, regulations get headlines; education programs on the dangers of saturated fats and how to find, buy, and cook better food—programs in which his department invests heavily—get yawns. I’ll be watching follow-up studies to see whether the cure for trans fats, which in many cases is to replace them with highly saturated fats, is worse than the disease.

And when the beleaguered cooks at Dunkin’ Donuts finally solve the riddle of removing trans fats, as New York City says they must by July of next year, I’ll be eager to learn how they did it. At the risk of revealing a rival’s trade secret, may I suggest oat bran and golden flaxseed?

Corby Kummer's work in The Atlantic has established him as one of the most widely read, authoritative, and creative food writers in the United States. The San Francisco Examiner pronounced him "a dean among food writers in America." Julia Child once said, "I think he's a very good food writer. He really does his homework. As a reporter and a writer he takes his work very seriously." Kummer's 1990 Atlantic series about coffee was heralded by foodies and the general public alike. The response to his recommendations about coffees and coffee-makers was typical--suppliers scrambled to meet the demand. As Giorgio Deluca, co-founder of New York's epicurean grocery Dean & Deluca, says: "I can tell when Corby's pieces hit; the phone doesn't stop ringing." His book, The Joy of Coffee, based on his Atlantic series, was heralded by The New York Times as "the most definitive and engagingly written book on the subject to date." In nominating his work for a National Magazine Award (for which he became a finalist), the editors wrote: "Kummer treats food as if its preparation were something of a life sport: an activity to be pursued regularly and healthfully by knowledgeable people who demand quality." Kummer's book The Pleasures of Slow Food celebrates local artisans who raise and prepare the foods of their regions with the love and expertise that come only with generations of practice. Kummer was restaurant critic of New York Magazine in 1995 and 1996 and since 1997 has served as restaurant critic for Boston Magazine. He is also a frequent food commentator on television and radio. He was educated at Yale, immediately after which he came to The Atlantic. He is the recipient of five James Beard Journalism Awards, including the MFK Fisher Distinguished Writing Award.